Question

In a magnetic field of 0.05T, area of a coil changes from 101 cm² to 100 cm² without changing the resistance which is 2Ω. The amount of charge that flow during this period is
(a) 2.5×10⁻⁶ coulomb
(b) 2×10⁻⁶ coulomb
(c) 10⁻⁶ coulomb
(d) 8×10⁻⁶ coulomb

Answer 1

answer : option (a) is correct.


explanation : we know, magnetic flux = magnetic field × cross sectional area .

so, induced emf can be produced by two methods. 1 . changing magnetic field
2. changing cross sectional area.

here magnetic flux is changed by changing cross sectional area.

so, formula is , $Q_{in}=\frac{\Delta\phi}{R}$ [ didn't include sign , just require to find magnitude]

= $\frac{B\Delta A}{R}$

where B is magnetic field, ∆A is change in cross sectional area and R is resistance of coil.

B = 0.05T, ∆A = (101 - 100) cm² = 1cm² = 10^-4 m² and R = 2ohms

so, $Q_{in}=\frac{0.05\times10^{-4}}{2}$

= 2.5 × 10^-6 coulombs

hence, option (a) is correct.

Answer 2

Answer:2.5 × 10^-6C

Explanation:dq=dphi/ R